Railway signaling apparatus



NOV. 26', 1940. SQRENSEN 2,222,804

RAILWAY SIGNALING APPARATUS Filed April 29, 1939 2 Sheets-Sheet 1 W la . L lb CI 37 fgll 9 T12 Z I Fig. 1. Sl-

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RAILWAY SIGNALING APPARATUS Filed April 29, 1939 2 Sheets-Sheet 2 W Ia, X

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INVENTOR Andrew o ensezz HIS Ai'TORNEY Patented Nov. 26, 1940 a r I 2,222,804

RAILWAY SIGNALING APBARATUS Andrew J. Sorensen, Edgewood Pa, assignor to The Union Switch & Signal Company, Swissvale, Pa, a corporation of Pennsylvania Application April 29, 1939, Serial No. 270,819

11 Claims. (or. 246 i1) My invention relates to railway signaling aping preferably interposed in the connection. The paratus, and more specifically to railway track alternating current suppliedthrough the medium circuit apparatus. of track transformer TF may-be of any con- I shall describe several forms of apparatus em- 'venient frequency. such as the usual commercial 5 bodying my invention, and shall then point out frequency of "69 cycles per second, or it" may be the novel features thereof in claims. of the frequency of 100 cycles per second such A feature of my invention is the provision of as commonly used in railway cab signaling sysnovel and improved means for a track circuit tem's. I I of an insulated track section wherewith a sub- An asymmetric unit 4,'such as, for example,

stantially uniform voltage throughout the track a copper oxide rectifier unit, is connected across section is obtained, and improved shunting senthe rails at the exit end of the section =W-X, sitivity of the track circuit provided While the the unit 3 being disposed with its high resistance amount of power consumed due to leakage is direction to oppose the flow of current from track relatively low. Another feature of my invention battery 2. j

is the provision of novel and improved means for The track relay for the track'circ'uit for sec- 15 a track circuit of an insulated track section for tion WX is a direct current neutral relay TR applying to the track rails an electromotive force Whose operating winding 27 is connected across having two predetermined components to a parthe rails at the entrance end of the section. ticular one of which a track relay is responsive The electro-motive forces created between the OFFICE .20 and the other of which is effective to break down rails of section by track battery 2 and the wheel-rail contact resistance when the sec track transformer TF pro duce a resultant election is occupied and a low resistance train shunt tromotiveforce which at any given instant isthe is assured. Again, a feature of my invention is vector sum of the two. That is, the resultant the provision of novel and improved apparatus electromotive force 'c'ontains two components one of the type here involved for control of signals predeterminedby the powersupplied by battery 25 of a wayside signal system. Other features and 2 and the'other predetermined by the power supadvantages of my invention will appear as the p d y tranSfOrmei I I specification progresses. The electromotiveforce across the rails as 'ef- In the accompanying drawings, Figs. 1, 2, 3 fected by battery 2 is a maximum at'the exit and 4 are diagrammatic views of four different end of'the section, gradually decreases and'is'30 forms of track circuit apparatus embodying my of a minimum value'at the entrance end of the invention. Fig. 5 is a diagrammatic view of ansection, whereas the electromotive force across j other form of track circuit apparatus embodying the rails as efiected by transformer TF is of amy invention when used with a three block four maximum value at the entrance end of the sec-Q .35 indication wayside signal system. tion, gradually decreases and is of a minimum In each of the several views, like reference Value at the exit end of the section. As stated characters designate similar parts. hereinbefore, the resultant electro-motive force Referring to Fig. 1, the track rails ia and Eb between the rails at any point in the track secof a stretch of railway over which traffic no-rtion is the vectorsum of these twoelectromotive 4o mally moves in the direction indicated by the forces. The two sources of power, track battery 40 arrow are formed by the usual insulated rail 2 and'track transformer TF, are so proportionedjoints with a track section WX which section that such resultant electrom'otive force has a is provided with a track circuit having trackway substantially uniform 'value' throughout the. sources of power connected across the rails at track sectionfthis resultant electromotiveforce predetermined points in the section. A track having a recurrent maximum or peak value bebattery 2 is connected across the rails at the exit cause of the alternating current component. end of section W-X over a resistor 3, the polar- The current sources are further so proportioned ity of battery 2 being predetermined as indicated as to produce a resultant electromotive 'force of by the plus and minus signs. A track transrelatively i p Vallle- QM former TF whose primary winding 5 is constantly The track relay TR which is a direct current supplied with alternating current from any conrelay is effectively energized only inresponse to venient source whose terminals are indicated as e ul efii Component of he resultant BX and CK has a secondary winding 5 conelectromotive force between the rails. 7 Thus, the nected across the rails at the entrance end of track relay .TB is energized in part'by power supsection WX, a current limiting resistor 1 beplied by battery 2 and in part bypower supplied by transformer TF. With section WX unoccupied, the unit 4 forms a low resistance path for the half cycle of the alternating electromotive force which causes rail Ia to be positive and rail lb to be negative, and forms a high resistance path for the half cycle of the alternating electromotive force which causes rail lb to be positive and rail la to be negative with the result that rectified current supplied from track transformer TF aids the energization of relay TR effected by the direct current supplied from track battery 2. It should be noted that the ohmic resistance of resistor 1 and secondary winding 6 is made sufficiently high to avoid diverting any material amount of direct current supplied by battery 2. Hence, when the section WXis unoccupied the direct current track relay TR is effectively energized and picked up closing front contact 9 which may be used to control a signal control circuit as desired.

When thesection WX is occupied by a train the maximum or peak value of the electromotive force produced by the sources of power breaks down the wheel-rail contact resistance and a relatively low train shunt is established so that the track circuit has a high shunting sensitivity and release of the track relay TR in response to occupancy of the track section is assured. Furthermore, because the electromotive force between'the rails is substantially uniform throughout the section the shunting sensitivity of the track circuit is substantially uniform in all points of the section.

It is clear that the leakage power consumed by the track circuit of track section WX is relatively low when compared with a track circuit having a single source of electromotive force at one end of the section. The voltage of such single source must be high to obtain the necessary voltage at the other end of the section to effectively energize a trackrelay and to effect a high shunting sensitivity so that the voltage through the greater part of the section is higher than required and excess leakage occurs.

, In Fig. 2, the railway is formed with an insulated track section WX having two sources of power connected across the rails at selected points of the section the same as in Fig. 1. The track battery 2 of the track circuit of track section WX of Fig. 2 is connected in series with the resistor 3 across the rails at the exit end of the section. The secondary winding 5 of track transformer TF and the winding of an alternating current relay AR are connected in series across the rails at the entrance end of the section. The direct current track relay TR of Fig. 2 is connected across the rails at the entrance end of the section over a front contact 8 of relay AR. The alternating current relay AR is adjusted so that the .leakage alternating current under dry ballast conditions is suflicient to effectively energize and pick up that relay closing front contact 8. Hence, relay AR is picked up at all times except in case of a failure of the alternating current power.

It is clear that the electromotive forces impressed on the railsby battery 2 and transformer TF produce a resultant electromotive force which is the vector sum of the two. The .two sources of power of Fig. 2 are so proportioned as to effect a'resultant electromotive force which is substantially uniform throughout the section, such re- When the section WX of Fig. 2 is unoccupied the direct current track relay TR is effectively energized and picked up in response to the current supplied by battery 2, that is, relay TB is energized in response to the direct electromotive force component of the resultant electromotive force. When the section is occupied, the maximum or peak values of the resultant electromotive force breaks down the wheel-rail contact resistance and high shunting sensitivity of the track circuit is obtained. Furthermore, the shunting sensitivity is substantially uniform at all points of the section because of the resultant electromotive force being substantially uniform in value throughout the section. Also the power losses due to ballast resistance is relatively low. In the event there is a loss of alternating current power, the relay AR is deenergized and released to open the connection to track relay TR with the result that relay TB. is released and such loss of power at once detected.

In Fig. 3, the track circuit of an insulated track section WX differs from that of Fig. 2 in that the secondary winding 6 of transformer TB is connected across the rails at approximately the mid point of the section, a resistor I being preferablyinterposed in the connection. The alternating current relay AR is connected across the rails at the entrance end of the section and controls at its front contact 8 the connection of the direct current track relay TR with the rails. It will be understood, of course, that the ohmic resistance of the winding of relay AR as well as the ohmic resistance of the path including resistor I and secondary winding 6 of transformer TF is in each case high enough to avoid diverting any material amount of direct current supplied by battery 2.

In Fig. 3, the two sources of power and the associated elements are so proportioned and adjusted that a resultant electromotive force is produced for the track circuit of the section which has characteristics similar to those described by the track circuits of Figs. 1 and 2.

Referring now to Fig. 4, the rails la and lb are formed with a track section WX having a track circuit provided with two sources of power connected with the rails at predetermined points of the section. 'In Fig. 4, a track battery 2 is connected across the rails at the exit end of the section by having one of its terminals connected with. rail lb over wire In and its other terminal connected with rail la over contact l2 of a code transmitter CT and a primary winding I 3 of a transformer Tl, both of which will be described hereinafter, and thence over a resistor l4 and wire IS. The track transformer TF of Fig. 4 has its secondary winding 6 connected across the rails at the entrance end of the section in the same manner as in Fig. l.

The code transmitter CT may be of any of the several well-known types and as here shown it is of the relay type. It is sufficient for this application to point out that when winding l6 of transmitter CT is energized a contact member I1 is operated to periodically engage a contact 12 at a predetermined rate, such as, for example, 75 times per minute, the contact l1l2 being closed for substantially one-half of each operating cycle of code transmitter CT and being opened for substantially one-half of each operating cycle. Furthermore, contact member I! is normally biased so that it is held in engagement with contact l2 when the winding [6 is deenergized. It follows that as long as the codetransmitter CT is operated, a direct electromotive force is periodically impressed upon the rails of section WX and when transmitter CT is inactive, non-interrupted direct electromotive force is applied to the rails.

In Fig. 4 the track relay for the track circuit is 'adirect current quick acting code following relay CF whose operating winding is connected across the rails at the entrance end of the section. Hence, the track relay CF is operated in response to the direct electromotive forces periodically produced across the track rails by battery 2 when the code transmitter CT is active and is inactive when the code transmitter is inactive, and furthermore it is non-responsive to the alternating electromotive forces supplied from the transformer TF. That is to say, the code following relay CF is operated in response to a particular one of the components of the resultant electromotive force and is non-responsive to the other component of such resultant electromotive force. When track relay CF is operating to alternately close-its front contact I8 and back contact I9, direct current from a source whose terminals are designated B and C is alternately supplied to two portions of the primary winding 29 of a transformer T2 to induce an alternating electromotive force in the secondary Winding 2! of transformer T2. The secondary winding 2! is connected with a winding of a control relay CR through a full wave rectifier 22. Consequently, relay CR, which is preferably slightly slow releasing in character, is energized and picked up closing a signal control circuit at its front contact 23 when periodic impulses of direct elec tromotive force are supplied to the track circuit from track battery 2 and the track relay CF is operated at a corresponding frequency.

When contact Il-IZ of code transmitter CT is closed the alternating electromotive force produced across the track rails by track transformer TF causes an alternating current to flow in the circuit which includes wire I5, resistor I4, primary winding I3 of transformer TI, contact I'II2 of transmitter CT, battery 2 and wire I0, and an alternating electromotive force is induced in the secondary winding 2 4 of transformer TI. Secondary winding 24 of transformer T1 is connected with the winding of a slow release relay RI through a full wave rectifier 25 with the result that relay RI is picked up closing front contact 26 when the section WX is unoccupied. Front contact 26 is interposed in a simple energizing circuit for the operating winding I6 of the code transmitter CT as will be readily understood by an inspection of Fig. 4.

It follows that when section W-X of Fig. 4 is unoccupied, the alternating current supplied through transformer TI during the periods the contact I'I-I2 of transmitter CT is closed causes relay RI to be picked up and energy is supplied to the operating winding I6 of transmitter CT causing the transmitter to be operated. With transmitter CT operated, the direct current code following relay CF is operated in response'to the direct electromotive force periodically applied across the rails from track battery 2 and the signal control relay OR is picked up.

It is apparent that the two sources of power for the track circuit of Fig. 4 create a resultant electromotive force which is the vector sum of the two, the same as described for Figs. 1, 2 and 3, except for the fact that the direct electromotive force is' periodically interrupted. Again the two sources of power are so proportioned as to create a resultant electromotive force which is substantially uniform in value throughout the section and has a high peak value.

When section WX of Fig. 4 is occupied, the

relay CF and the alternating current is shunted away from the primary winding I3 of transformer TI. Hence, relay CF ceases to operate and the control relay CR in turn is deenergized and released to govern the signal control circuit. Also, the relay RI is deenergized and released causing the code transmitter CT to be inactive, its contact member Il remaining stationary in engagement with contact I2 due to the bias of the code transmitter. When the train moves out of section WX, the alternating current flowing in primary winding I3 causes relay RI to be picked up closing front contact 26 and code transmitter CT is in turn operated at a corresponding frequency for operating track relay CF to control relay CR and in turn close the signal control circuit.

It is to be observed that in the event of a loss of alternating current power, the relay RI is de-.

tive electromotive forces both of which are applied across the rails at the exit end of the section. The resultant electromotive force istherefore the vector sum of the two forces and this resultant electromotive force is in turn characterized by recurrently high peak values which break down the rail film resistance when the section is occupied so that a high shunting sensitivity for the track circuit prevails.

The track circuit for section WX of Fig. 5 is used to control a wayside signal system. Hence, the railway would, of course, be formed with consecutive track sections each of which is provided with av track circuit similar to the track circuit for section WX. The apparatus for the track circuit of section WX and a portion of the apparatus for the track circuit for the section next in advance of section WX only are 4 shown for the sake of simplicity since such is sufficient for a full understanding of this form of apparatus embodying my invention and how it can be used to control a wayside signal system.

The means for applying two electromotive forces to the track circuit of section WX of Fig. 5 consists of a track battery 2, a code transmitter CT and a track transformer TFI' together with the necessary circuits.

The code transmitter CT is preferably of the relay type the same as in Fig. 4 and its operating winding I6 is permanently connected with the source of current Whose terminals are B and C and is hence continuously active to operate its contact member I? between contacts I2 and 48 at a predetermined rate which rate I have assumed hereinbefore for illustration to be '75 times per minute. The contacts I2 and 48 are connected in multiple and are interposed in any one of aplurality of different circuits to be effectively shunted away from the code following later described. Hence, the circuit in which contacts l2 and 48 are interposed under a specific condition is periodically interrupted during each time that contact member H is in transit between its two positions, the circuit being closed when either contact I'll2 or l148 is closed and hence is closed during the major portion of each operating cycle of the transmitter. E'ach ofthe different circuits in which the contacts l2 and 48 of the code transmitter are included also includes the track battery 2 and the primary winding 49 of transformer TFI as will be pointed out hereinafter. Hence, the current flowing in primary winding 49 from battery 2 through contact I'l-l2 or Il-48 is momentarily interrupted during each interval the contact member I? is in transit and an electromotive force is induced in the secondary winding 50 of transformer TFI. That is to say, when either contact I 'll-2 or I'l-48 is closed and direct current flows in the primary winding 49, magnetic energy is stored in the transformer TFI so that when contact member I I is moved from one contact to the other and the circuit is momentarily interrupted an electro-motive force is induced in the secondary winding 50 of transformer 'I'Fl. The secondary winding 59 is connected across the rails Ia and lb over wires 56 and 51, a condenser C2 of relatively large capacity being interposed in wire 51. The complete circuits and manner whereby two electromotive forces are applied to the rails, one from track battery 2 and one from transformer TFI, will be explained when the operation of the apparatus of Fig. 5 is described.

The relay means for the track circuit of section WX of Fig-5 includes a direct current polarized track relay XTR, a code following relay XCF, a transformer XT2 and a control relay XCR. The code'following relay XCF is connected across the rails at the entrance end of the section WX through a blocking condenser XCI and is preferably of the quick acting type. With relay XCF operated in a manner to later appear to alternately close its contacts 6334 and 63-35, direct current is alternately supplied to two portions of the primary winding 29 of transformer XT2 to induce an electromotive force in the secondary winding 3!] of that transformer. The secondary winding 39 is connected to the winding of relay XCR through a rectifier 31. Hence, the electromotive force induced in the secondary winding 39 is rectified and applied to the winding of control relay XCR. Relay XCR governs at the front contact 32 the connection of direct current track" relay XTR with the track rails as will be readily understood by an inspection of Fig. 5.

Looking at the left-hand end of Fig. 5, a code following relay WCF and a direct current polarized track relay WTR are associated with the track circuit for the section next in advance of section WX and are connected across the rails of the section next in advance in the same manner that relays XCF and XTR are connected with the rails of section WX. That is to say, relay WCF is connected with the rails of the section next in advance through a blocking condenser WC! and when operated causes a control relay WCR to be energized and picked up while the direct current polarized relay WTR is connected across the rails of the section in advance over front contact 331 of relay WCR.

Wayside signals XS and WS which govern traffic through track section WX and the section next in advance, respectively, are provided.

The signals XS and WS may be of any of thestandard types and in this instance are color light signals capable of displaying four different indications. Looking at signal 'WS, it comprises two groups of lamps, the top group having va green lamp G, a yellow lamp Y and a red lamp R; and the bottom group having a green lamp G and a red lamp R. The operating circuits for signal WS are controlled by relays WTR and WCR associated with the track circuit for the section next in advance. These operating circuits may be of any of the standard types since their specific arrangement forms no part of my present invention.

In Fig. 5, the operating circuits for signal WS are as follows: when relay WCR is picked up and relay WTR is picked up at its normal polar or right-hand position, the G lamp of the top group of lamps and the R lamp of the bottom group of lamps of signal WS are illuminated so that signal WS displays a green light over a red light for a clear signal indication. The circuit for lamp G of the top group can be traced from terminal B over front contact 36 of relay WCR, front contact 31 of relay WTR, normal polar contact 38 of relay WTR, lamp G and terminal C. The circuit for the R lamp of the bottom group of lamps extends from terminal B over front contact 39 of relay WCR, front contact 40 of relay WTR, normal polar contact 4| of relay WTR, lamp R and terminal C. When relay WCR is picked up and relay WTR is picked up at its reverse polar position, the Y lamp of the top group of lamps and the G lamp of the bottom group of lamps are illuminated so that signal WS displays a yellow light above a green light for an approach medium signal indication. The circuit for the Y lamp extends from terminal B over front contacts 36 and 31 of relays WCR and WTR, respectively, reverse polar contact 42 of relay WTR, lamp Y and terminal C. The circuit for the G lamp of the bottom group of lamps includes terminal B, front contacts 39 and 40 of relays WCR and WTR, respectively, reverse polar contact 43 of relay WTR, lamp G and terminal C.

Again, when relay WCR is picked up and relay WTR is released, the Y lamp of'the top group of lamps and the R lamp of the bottom group of lamps are illuminated and the signal WS displays a yellow light over a red light for an approach signal indication. The circuit for the lamp Y includes terminal B, front contact 36 of relay WCR, back contact 44 of relay WTR, lamp Y and terminal C; and the circuit for the R lamp involves terminal B, front contact 39 of relay WCR, back contact 45 of relay WTR, lamp R and terminal C.

When relay WCR is released, the R lamp of each of the two groups of lamps is illuminated and signal WS displays a red light over a red light for the stop signal indication. The circuit of the top lamp R includes terminal B, back contact 46 of relay WCR, lamp R and terminal C; and the circuit for the lamp R of the bottom group of lamps includes terminal B, back contact 41 of relay WCR, lamp R and terminal C.

The operating circuits for signal XS are controlled by relays XCR and XTR in the same manner as the circuits for signal WS are controlled by relays WCR and WTR and only certain portions of the circuits for signal XS are shown for the sake of clarity since this much of the circuits is sufficient for a full understanding of the invention.

In describing the operation of the apparatus of Fig. 5, I shall first assume the section next in advance of section W-X is occupied so that relayWCF is made inactive causing relay WCR to be deenergized and released as well as relay WTR. being deenergized andreleased. With relays WCR and WTR both released, the wayside signal WS displays the stop signal indication'as explained hereinbefore. Also, current now flows from the positive terminal of battery 2 over a resistor 5i, back contact 52 of relay WCR, primary winding 49 of transformer TFI either contact Ill-42 or II48 of code transmitter CT and to the negative terminal of battery 2. Since this circuit including primary winding 49 is momentarily interrupted each time the contact member I! is in transit between contacts l2 and 48, the magnetic energy stored in transformer TB! decays and produces an electromotive force in the secondary winding 50 of that transformer, the wave form of such electromotive force in .efiect consisting of a single half-cycle of short duration. The parts are so proportioned that each such impulse of electromotive force is of relatively high peak voltage as well as of short duration. This electromotive force induced in secondary winding 58 is applied across the rails of section W-X through condenser C2, causing an impulse of current to fiow in the winding of relay XCF through condenser XCI with the result that contact 6335 of relay XCF is momentarily closed. Consequently, the relay XCF is operated at a frequency corresponding to the frequency at which the code transmitter CT is operating and in turn causes the control relay XCR to be picked up closing the connection of track relay XTR with the track rails at front contact 32. It should be noted that the impedance of track relay XTR, due to its construction, is high and that relay therefore does not divert an appreciable amount of power of the impulse which operates relay XCF' as well as not being responsive to such impulses of electromotive force. It follows that with the section next in advance occupied, impulses of electromotive force from transformer TFl' only are applied to the rails of section WX with the result relay XCR is picked up and relay XTR is-released. With relay XCR, picked up and relay XTR released the associated signal XS is caused to display an approach signal indication, the operating circuits for signal XS being the same as described for signal WS.

I shall next assume that the section next in advance of section WX is unoccupied and the second section in advance is occupied so that relay WCR is picked up but relay WTR is released. Under this condition, current flows from the positive terminal of battery 2 over back contact 53 of track relay WTR, wire 56, rail lb, wire 55, winding of relay XTR, front contact 32 of relay XCR, wire 54, rail la, wire 5?, back contact 58 of relay WTR, front contact 59 of relay WCR, primary winding 49 of transformer TF1, either contact l'll2 or I'l-48 of transmitter CT and to battery 2. Direct current flows in this circuit during each interval either contact I'l-l2 or H--48 is closed, which intervals it will be recalled are relatively long with the result that the direct current track relay XTR is eifectively energized thereby and picked up. The polarity of such current which is effective to close the reverse polar contacts of relay XTR, I shall term reverse polarity. Such direct ourrent is substantially blocked by condenser X0! and does not afiect the code following relay XCF. This circuit is momentarily interrupted each time contact member 11 of transmitter CT is in transit between its two positions and an electromotive force impulse is induced in the secondary winding 50, the same as described hereinbefore, and which impulse of electromotive force is applied from secondary winding 5|] to the rails of the section WX causing an impulse of current to flow through condenser XCI to momentarily pick up the code following. relay XCF with the result that the control relay XCR- is energized and picked up. With relay XCR picked up and relay XTR picked up at its reverse position, the signal XS is caused to display an approach medium indication.

Next I shall assume that the first two sections in advance of section WX are unoccupied and the third section in advance is occupied so that relay WCR is picked up and relay WTR. is picked up at its reverse position. A circuit can now be traced from the positive terminal of battery 2 over front contact 60 of relay WTR, wire 51, rail la, wire 54, front contact 32 of relay XCR, winding of relay XTR, wire 55, rail lb, wire 56, front contact (H of relay WTR, front contact 59 of relay WCR, primary winding 49 of transformer TFI, either contact H-l2 or contact ll48 of code transmitter CT and to the negative terminal of battery 2. The direct current flowing in this circuit during each interval either contact I'll2 or |148 is closed is effective to energize and pick up the relay XTR. The polarity of the current is now of normal polarity so that relay XTR is closed at its normal polar position. The circuit is momentarily interrupted each time the contact member I! is in transit with the result that an impulse of electromotive force is induced in secondary winding 50 of transformer TFI which impulse of electromotive force is applied across the rails and causes a current impulse to flow in the winding of relay XCF to operate that relay so that the control relay XCR is energized and picked up. With relay. XCR picked up and relay XTR picked up at its normal position the signal XS is caused to display -a clear signal indication.

Again assuming that the three sections next in advance of section W-X are unoccupied so that relay WCR is picked up and relay WTR is picked up at its normal position, current of normal polarity is again supplied to the track circuit for section W-X and relay XTR is energized at its normal polar position. Again each time the contact member I! of transmitter CT is moved from one position to the other an impulse of electromotive force is induced in the secondary winding 50 of transformer TFI which electromo- I efiected between the rails by battery 2 and that.

eifected from secondary winding 50 of transformer TF1 are distinctive in character and cooperate to create a resultant electromotive force which is characterized by periodically high peak values. Hence, when the section W-X is occupied the peak value of the resultant electromo tive force breaks down the resistance of the wheel-rail contacts and a high shunting sensi tivity for the track circuit is provided with the result that both relays XCF and -XTR are deenergized causing signal XS to display a stop indication, relay XTR being also disconnected from the rails when relay XOR. is released.

In order to stabilize the track circuit of Fig. 5 and avoid too'great a variation of the current flowing in the primary winding 49 of transformer TFI between dry and wet ballast conditions, a resistor 64 is preferably connected between the rails. Resistor 64 is so chosen as to cause approximately the same peak values of the electromotive force induced in the secondary winding 50 under dry and wet ballast conditions with the result that a satisfactory shunting sensitivity of the track circuit is effected for all ballast conditions within the usual operating limits. It should be pointed out that resistor 64 if broken does not cause a dangerous failure. At low ballast resistance, the resistor 64 is high enough to make little or no appreciable difference in the operation of the track circuit. If resistor 64 becomes disconnected at high ballast resistance, the current flowing in primary winding 49 is reduced and the electromotive force induced in secondary winding 50 correspondingly reduced so that the current impulses operating relay XCF are materially reduced in magnitude and should relay XCF fail to respond then both relays XCR and XTR become deenergized and released and the most restrictive indication of signal XS is displayed.

Although I have herein shown and described only certain forms of railway signaling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, an insulated track section, a source of unidirectional. current connected across the rails at one end of said section, a direct current track relay connected across the rails at the other end of said section effectively energized by said unidirectional current when the section is unoccupied, a source of alternating current connected across the rails'of the section to supply to the rails current of relatively high instantaneous voltages for breaking down the rail film resistance when the sectionkis occupied to aid the shunting of said track relay, another relay having connection with the rails of said section effectively energized by said alternating current, and means including a contact of said other relay .for controlling the supply of unidirectional current to said track relay.

2. In combination, an insulated track section, a track battery connected across the rails at one end of said section, a track transformer having a primary winding supplied with alternating current, an alternating current relay, means to connect a secondary winding of said transformer and a. winding of said relay in series across the rails at the other end of said section, and a direct current track relay having its Winding connected across the rails at said other end of said section over a front contact of said alternating current relay.

3. In combination, an insulated track section, a track battery, a normally active code transmitter, a first transformer, means including a contact of said transmitter and a primary winding of said transformer to connect said battery across the rails at one end of said section to supply recurrent impulses of direct current'to the rails, a control relay, means including a rectifier to connect a winding of said control relay across the secondary winding of said first transformer for energizing said relay when alternating current flows in the primary winding of said transformer, means including a front contact of said control relay to energize said code transmitter, a track transformer having its primary winding supplied with alternating current and its secondary winding connected across the rails at the other end of saidsection for energizing said control relay when the section is unoccupied, a direct current code following relay connected across the rails at said other end of the section effectively operated by said recurrent impulses of direct current when the section is unoccupied, and signaling means controlled by said code following relay.

4. In combination, an insulated track section, a track battery, a normally active code transmitter, a track transformer, means to connect said battery in series with a primary winding of said transformer across the rails at the exit end of said section over a contact of said transmitter to effect a direct electromotive force across the rails which is periodically interrupted, means including a condenser to connect a secondary winding of said transformer across the rails at the exit end of said section to periodically effect across the rails an impulse of electromotive force of relatively short duration and high peak voltage, a code following relay having its winding connected in series with another condenser across the rails at the entrance end of the section effectively operated in response to said impulses of electromotive force, a direct current relay having its winding connected across the rails at the entrance end of said section effectively energized by said direct electromotive force, and a signal circuit jointly controlled by said two relays.

5. In combination, an insulated track section, a track battery, a normally active code transmitter, a track transformer, means controlled by traffic in advance of said section to connect said battery in series with a primary winding of said transformer across the rails at the exit end of said section over a contact of said transmitter to effect periodically interrupted direct electromotive force of either positive polarity or negative polarity in response to two different traffic conditions in advance, means including a condenser to connect a secondary winding of said transformer across the rails at the exit end of the section to effect periodic impulses of electromotive force of relatively short duration and high peak voltage due to operation of said transmitter, a code following relay having its winding connected in series with another condenser across the rails at the entrance end of the'section effectively operated in response to said impulses of electromotive force, a direct current polarized relay having its winding connected across the rails at the entrance of said section effectively energized in response to said direct electromotive force, and two signaling circuits jointly controlled by said two relays one closed when the polarized relay is energized at normal polarity and the other closed when the polarized relay is energized at reverse polarity.

6. In combination, an insulated track section, a track battery, a normally active code transcondenser to connect a secondary winding of said transformer across the rails at the exit end of said section, means controlled by three different traffic conditions in advance of said section to connect said battery in series with a primary winding of said transformer over a contact of said transmitter to effect periodic impulses of electromotive force across the rails in response to a first one of the trafiic conditions and to connect' said battery in series with said primary winding across the rails at the exit end of the section over said transmitter contact to effect direct electromotive force of either normal polarity or reverse polarity in response to either a second or a third one of said traffic conditions respectively, a code following relay having its winding connected in series with another condenser across the rails at the entrance end of the section effectively operated in response to said impulses of electromotive force, a direct current polarized relay having its winding connected across the rails at the entrance end of the section over a front contact of said code following relay effectively energized in response to said direct electromotive force, and three diflerent signaling circuits selectively controlled by said two relays.

'7. In combination, an insulated track section, a transformer, a code transmitter, a source of direct current connected across the rails at one end of said section through a primary winding ofsaid transformer in series with a contact of said code transmitter for supplying coded direct current to the rails when said code transmitter is operated, a code following track relay connected across the rails at the other end of said section effectively operated by such coded direct current when the section is unoccupied, a signaling circuit controlled by said track relay and closed when the relay is operated, a control relay having connection to a secondary winding of said transformer effectively energized and picked up when an alternating current flows in said primary winding, a source of alternating current connected across the rails at said other end of said section to energize said control relay when the section is unoccupied and which alternating current is effectively shunted to deenergize said control relay when the section is occupied, and an operating circuit including a front contact of said control relay for operating said code transmitter to discontinue operation of the code transmitter when the section is occupied as an aid in rendering said code following relay responsive to occupancy of the section.

8. In combination, an insulated track section, a normally active code transmitter, a transformer, a source of direct current connected in series with a primary winding of said transformer across the rails at one end of said section over a contact of said code transmitter to supply periodically interrupted direct current to the rails, a direct current track relay having connection to the rails at the other end of the section for energization thereof by said interrupted direct current when the section is unoccupied,

signaling means controlled over a contact of said track relay, means including a condenser to connect a secondary winding of said transformer across the rails at the other end of the section to supply a current impulse of relatively short duration and high peak voltage each time said direct current is interrupted as an aid in breaking down cupied, a code following relay having a winding connected in series with another condenser across the rails at said other end of the section effectively operated by such current impulses when the section is unoccupied, and a contact governed by said code following relay interposed in said connection of said track relay to the rails to complete such connection only when the code following relay is operated.

9. In combination, an insulated track section, a normally active code transmitter, a transformer, a source of direct current, means including a contact of said code transmitter to connect said current source and a primary winding of said transformer across the rails at one end of said section to supply periodically interrupted direct current to the rails, a direct current track relay having connection to the rails at the other end of the section effectively energized by said interrupted direct current when the section is unoccupied, and a secondary winding of said trans former connected in series with a condenser across the rails at said one end of the section to supply a current impulse of relatively high peak voltage each time said direct current is interrupted as an aid in breaking down the rail film resistance and shunting said track relay when the section is occupied.

10. In combination, an insulated track section, a trackway source of power having connection to the rails at one end of the section to supply a direct electromotive force to the rails, a track relay having connection to the rails at the other end of the section effectively energized by said supply of direct electromotive force when the section is unoccupied, another trackway source of power having connection to the rails of the section to supply a periodic electromotive force across the rails which is incapable of effectively energizing said relay and which periodic electromotive force is of relatively high peak voltage to provide a high shunting sensitivity for said track relay by breaking down the rail film resistance, when the section is occupied, and an-' other relay receiving energy from said other trackway source of power and having a contact which controls the supply of said direct electromotive force to permit energization of said track relay only when said other trackway source of power is supplying said periodic electromotive force to the rails.

11. In combination, an insulated track section, a track battery connected to the-rails at one end of the section to supply unidirectional current to the rails, a direct current track relay connected to the rails at the other end of the section effectively energized by said supply of unidirectional current when the section is unoccupied, other means connected to the rails of the section to supply a periodic current to which said track relay is non-responsive and which periodic current serves to break down the rail film resistance and aid the shunting of said track relay when the section is occupied, and another relay energized by such periodic current received from said other means and having a front contact which controls the supply of said unidirectional current to cause release of said track relay when said other means fails to supply said periodic current. 7

ANDREW J. SORENSEN.

the rail film resistance when the section is 

